This invention relates to an active vibration suppressing system, called an active damper, for suppressing vibration of a structure on the basis of a drive reaction force of a movable mass. In another aspect, the invention concerns a technology for removing or reducing an adverse influence of floor vibration to a positioning operation in a semiconductor exposure apparatus, for example, by using such an active damper.
In order to meet further miniaturization of a semiconductor device, very high requirements are being applied to a vibration environment such as a floor on which a semiconductor exposure apparatus is placed. This is because, if vibration of the floor, for example, is transmitted into the semiconductor exposure apparatus, it causes an error in measurement through a high precision measuring system therein or a degradation in precision of a positioning mechanism therein. Finally, it results in deterioration of exposure precision.
Because any vibration of a floor on which a semiconductor exposure apparatus is placed applies a notable influence to the exposure precision, for example, the exposure apparatus itself should have a function for blocking the floor vibration. To this end, a major structure of recent semiconductor exposure apparatuses is supported by using an active anti-vibration unit. Use of an anti-vibration unit of active type is effective to enlarge a high-frequency vibration removal region. Additionally, by detecting the floor vibration and by driving an actuator inside the active anti-vibration unit, for supporting the major structure while suitably processing the vibration signal, transmission of floor vibration into the major structure can be canceled. A technology called floor vibration feed forward or ground vibration feed forward, can be applied. Further, any oscillation of the major structure within the semiconductor exposure apparatus, resulting from drive of a movable mechanism such as a wafer stage, for example, can be suppressed by appropriately processing a drive signal for that mechanism and by driving the actuator inside the active anti-vibration unit.
However, if transmission of floor vibration to the major assembly structure cannot be suppressed to a predetermined level or lower even with optimal adjustment of the active anti-vibration unit of the semiconductor exposure apparatus as described above, then any vibration reducing measures should be made to the floor itself. More specifically, a structural member such as a beam, for example, which forms the floor, may be reinforced. Alternatively, beams which form the floor may be structurally reinforced such as with concrete to increase the mass and also to apply a damping function.
However, such floor reinforcing construction necessarily disturbs a clean environment inside a clean room where a semiconductor exposure apparatus is to be placed. Making such floor reinforcing construction to a clean room which is being used for device production is, therefore, substantially impractical.
Problems attributable to floor vibration will be uncovered after an expensive and heavy semiconductor exposure apparatus is mounted. Although some of them may be met by parameter tuning in an anti-vibration unit used in the semiconductor exposure apparatus, there remain adverse influences not removed by such parameter tuning.
It is an object of the present invention to provide a solution for such inconveniences. More specifically, it is an object of the present invention to provide an active vibration suppressing system by which adverse influences of vibration of a floor or of any other structural member to a positioning mechanism or the like can be removed or reduced. Thus, the vibration suppressing system of the present invention is very effective in a case wherein inconveniences resulting from floor vibration cannot be removed or reduced by parameter tuning of an anti-vibration unit, or a case wherein a reinforcing construction to a floor or any other structural member is difficult to do.
In accordance with an aspect of the present invention, there is provided a vibration suppressing system, comprising: a structural member with respect to which vibration suppression is to be executed; a movable member; an actuator for moving said movable member; a vibration sensor for measuring vibration of said structural member; and a controller for driving said actuator on the basis of an output of said vibration sensor.
In one preferred form of this aspect of the present invention, said actuator comprises a linear motor.
The vibration sensor may comprise an acceleration sensor. The system may further comprise a displacement sensor for measuring a movement distance of said movable element, and a movable element vibration sensor for measuring vibration of said movable element. The control for the vibration suppression may be made on the basis of an output of said vibration sensor, and a position of said movable element may be controlled on the basis of an output of said displacement sensor, wherein a control for vibration suppression may be made on the basis of an output of said movable element vibration sensor.
The vibration sensor may comprise a velocity sensor, and the system may further comprise a displacement sensor for measuring a movement distance of said movable element, and a movable element vibration sensor for measuring vibration of said movable element. The control for the vibration suppression may be made on the basis of an output of said vibration sensor, wherein a position of said movable element may be controlled on the basis of an output of said displacement sensor, and wherein a control for vibration suppression may be made on the basis of an output of said movable element vibration sensor.
The system may further comprise a compensator for applying a gain to an output of said velocity sensor. There may be a plurality of movable elements each as aforesaid.
The movable element may be oscillated at a predetermined frequency, in a state in which a control is being applied thereto while the same is at a neutral position.
The movable element may be moved in a vertical direction, or it may be moved in a horizontal direction. The movable element may be moved in synchronism with an operation of an exposure apparatus.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: a vibration suppressing system including (i) a movable member, (ii) an actuator for moving said movable member, (iii) a vibration sensor for measuring vibration of said structural member, and (iv) a controller for driving said actuator on the basis of an output of said vibration sensor; and a stage for positioning a wafer.
In one preferred form of this aspect of the present invention, said vibration suppressing system is mounted on at least one of a portion adjacent to said stage, a structural member of said exposure apparatus, a floor on which said exposure apparatus is disposed, and a structural member constituting the floor.
The apparatus may further comprise an illumination system, wherein said vibration suppressing system may be disposed at or adjacent to a structural member of said illumination system.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: applying a resist to a wafer; exposing the wafer by use of an exposure apparatus as recited above; and developing the exposed wafer.
In accordance with a further aspect of the present invention, there is provided an acceleration sensor, comprising: a variable resistance type acceleration sensor; a differential amplifier circuit, wherein a signal from said variable resistance type acceleration sensor is to be applied to said differential amplifier circuit; and a band-pass filter including a combination of a low-pass filter and a negative feedback based on an integration circuit.
In one preferred form of this aspect of the present invention, said variable resistance type acceleration sensor, said differential amplifier circuit and said band-pass filter are mounted on one and the same circuit board.
The acceleration sensor may further comprise an offset correcting circuit and a gain adjusting circuit.
The variable resistance type acceleration sensor, said differential amplifier circuit, said band-pass filter, said offset correcting circuit and said gain adjusting circuit may be mounted on one and the same circuit board.
In accordance with a yet further aspect of the present invention, there is provided a vibration suppressing system, comprising: an actuator having a fixed portion and a movable portion, said movable portion being movable relative to said fixed portion; and an acceleration sensor including a variable resistance type acceleration sensor, a differential amplifier to which a signal from said variable resistance type acceleration sensor is to be applied, and a band-pass filter having a combination of a low-pass filter and a negative feedback based on an integration circuit; wherein said acceleration sensor is mounted on at least one of said fixed portion and said movable portion.
The vibration suppressing system may further comprise a detector for detecting a relative position of said fixed portion and said movable portion.
The actuator may serve to suppress vibration of a structural member on the basis of a drive reaction force of said movable portion. The fixed portion may have a coil, and the movable portion may have a magnet.
In accordance with a still further aspect of the present invention, there is provided an exposure apparatus, comprising: an illumination system; a stage for carrying a wafer thereon and for positioning the wafer; and a vibration suppressing system as recited above, wherein said vibration suppressing system is disposed at at least one of said illumination system, a portion adjacent to said stage, a floor on which said exposure apparatus is mounted, and a structural member constituting the floor.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.